Optic-nerve-transmitted eyeshine, a new type of light emission from fish eyes

Abstract

BackgroundMost animal eyes feature an opaque pigmented eyecup to assure that light can enter from one direction only. We challenge this dogma by describing a previously unknown form of eyeshine resulting from light that enters the eye through the top of the head and optic nerve, eventually emanating through the pupil as a narrow beam: the Optic-Nerve-Transmitted (ONT) eyeshine. We characterize ONT eyeshine in the triplefin blenny Tripterygion delaisi (Tripterygiidae) in comparison to three other teleost species, using behavioural and anatomical observations, spectrophotometry, histology, and magnetic resonance imaging. The study’s aim is to identify the factors that determine ONT eyeshine occurrence and intensity, and whether these are specifically adapted for that purpose.ResultsONT eyeshine intensity benefits from locally reduced head pigmentation, a thin skull, the gap between eyes and forebrain, the potential light-guiding properties of the optic nerve, and, most importantly, a short distance between the head surface and the optic nerves.ConclusionsThe generality of these factors and the lack of specifically adapted features implies that ONT eyeshine is widespread among small fish species. Nevertheless, its intensity varies considerably, depending on the specific combination and varying expression of common anatomical features. We discuss whether ONT eyeshine might affect visual performance, and speculate about possible functions such as predator detection, camouflage, and intraspecific communication.Electronic supplementary materialThe online version of this article (doi:10.1186/s12983-017-0198-9) contains supplementary material, which is available to authorized users.

Visual modelling supports the potential for prey detection by means of diurnal active photolocation in a small cryptobenthic fish

“…12 . While these reflectors would not improve vision in dim light such as would tapetum lucidum and stratum argentum 41 , they would normally help camouflage the gammarid eye by making the otherwise black, photon-absorbing, eye look more like the substrate by reflecting some of the sidewelling light field 12 . Overall eye reflectance, within the 400 to 700 nm wavelength range and illuminated with a coaxial light source (epi-illumination), was on average 9.87, n = 18; Fig 3 ).…”

Daytime eyeshine contributes to pupil camouflage in a cryptobenthic marine fish

“…Like most scorpionfish, it features prominent eyes with a translucent retinal pigment epithelium resulting in daytime eyeshine ( Fig. 1) 6,12 . We caught 15 individuals in Calvi (Corsica, France) between 5 and 20 m depth under the general permit of STARESO (Station de Recherches Sous Marines et Océanographiques).…”

“…In the light-adapted state of the eye, the melanosomes of the retinal pigment epithelium enter the cell processes between the cones, clearing the way for light that passed through the receptor layer to also penetrate the translucent choroid 1,6 and reach the stratum argenteum. This light is reflected out of the pupil, generating a type of eyeshine termed Stratum Argenteum Reflected (SAR) eyeshine 12 . Another consequence of choroid translucency is that down-welling light that penetrates the dorsal part of the eye can be transmitted through the sclera and choroid and out through the pupil.…”

“…Another consequence of choroid translucency is that down-welling light that penetrates the dorsal part of the eye can be transmitted through the sclera and choroid and out through the pupil. This can result in a second type of eyeshine described as Pigment Epithelium Transmitted (PET) eyeshine 12 . While the translucency of the sclera and choroid has been already documented for these fishes 9,13 , pupil eyeshine has always been assumed to be the exclusive result of SAR eyeshine.…”

Craniofacial skeleton of MEXICAN tetra (Astyanax mexicanus): As a bone disease model

“…Several teleost fish species have already been identified as animal models for craniofacial research. This includes zebrafish (Yelick and Schilling, ; Stock, ; Mork and Crump, ), medaka (Kimura et al, ; Atukorala et al, ; Witten et al, ), cichlids (Fraser et al, ; Powder and Albertson, ), stickleback (Kimmel et al, ; Ellis et al, ), carp (Gidmark et al, , ), Polypterus (Vandenplas et al, ; Noda et al, ) and many others (Meredith and Butler, ; Ferry et al, ; Staab et al, ; Lyon et al, ; Edds‐Walton et al, ; Fritsch et al, ; Thiery et al, ).…”